1. Field of the Invention
The present invention relates to a numerical controller for controlling a machine and, more particularly, to a numerical controller that has a means for monitoring signals from a plurality of sensors that monitor states at individual places of a machine so as to determine whether the states at these places and the numerical controller are normal or abnormal from detected information obtained from the plurality of sensors and from internal information about the numerical controller.
2. Description of the Related Art
The spindle of a machine tool and a robot arm may unexpectedly strike against an object due to program error or an operator mistake. If this type of strike occurs, the structure itself of the spindle or robot arm or the motor for driving the spindle or robot arm causes a failure. The failure then affects machining precision and operation precision. Accordingly, if a strike occurs, it is desirable to stop and check the machine tool or robot.
To locate the cause of a strike, Japanese Patent Application Laid-Open No. 2008-176559, for example, discloses a technique by which when a signal detected by a vibration sensor becomes large, information about the internal speed and position of the numerical controller is also recorded.
In the summer and rainy season during which humidity is high, if an alarm occurs when a machine is turned on in the morning during which temperature is low, it has been determined from experience that an abnormal condition might have been caused by dew condensation.
In the technology disposed in Japanese Patent Application Laid-Open No. 2008-176559 described above, however, occurrence of a strike is just determined if a difference produced by a signal detected by any one of a plurality of vibration sensors disposed on the machine exceeds a preset threshold, and detected information obtained from the plurality of sensors and the internal information about the numerical controller are not combined in the process so as to determine whether an abnormal condition has occurred in the machine. That is, the fact that the machine has caused a strike can be detected, but the cause of the alarm cannot be located.